1. Field of the Invention
This invention relates generally to fluid handling and more specifically to line condition change responsive valves.
2. Discussion of the Prior Art
In braking systems using fluid pressure, fluid is generally supplied to the system by a compressor producing and feeding fluid under pressure to one or more fluid pressure reservoirs. The fluid pressure is stored in a main reservoir to be supplied on demand to braking components in the system, and also in an auxiliary reservoir to supply auxiliary fluid pressure operated devices. Generally a one-way check valve in the system, as is well known, permits fluid under pressure to pass in one direction from the compressor into either reservoir encountering nominal, if any, resistance but not in the opposite direction from the reservoirs back to the compressor. Once pressure across the check valve is substantially equal the check valve closes and is opened only to permit fluid pressure to pass through the valve when pressure on the compressor side of the valve is greater than pressure on the reservoir side of the valve. In this type of arrangement, pressure on the reservoir side of the valve would ordinarily never exceed the pressure on the compressor side of the valve as long as the compressor is operating to produce a pressure output. Should the compressor cease to produce pressure for some reason, and permit pressure on the reservoir side of the valve to exceed pressure on the compressor side, the valve, due to its one-way construction would prevent the escape of reservoir pressure, at least across the valve. It can be seen from the foregoing that as long as the compressor is producing pressure to the system fluid, the system reservoir fluid pressure should remain constant and that when system reservoir pressure begins to drop due to use of its stored pressure reserve, the check valve will open to receive fluid under pressure from the compressor to restore the system reservoir pressure. One shortcoming of having only a one-way check valve between a compressor and a reservoir is that in the event of a leakage to atmosphere of, for example, the auxiliary reservoir pressure, direct leakage would result in that the fluid pressure output of the compressor would meet no substantial resistance in encountering the check valve at the auxiliary reservoir. Thus, none of the fluid pressure output of the compressor would be available to replenish the main reservoir supply when needed and eventually no fluid pressure would be available for braking operations. It would be of benefit to fluid pressure braking systems to supply fluid under pressure to the auxiliary reservoir through a protecting device capable of limiting the possible loss of fluid pressure from the fluid pressure source to some predetermined minimum value so that some fluid pressure output of the compressor would be available to replenish the main reservoir supply for needed braking operations.